The bacterium appeared on the planet millions of years before humans, and scientists are certain it will outlast us too. It's practically guaranteed that salmonella will keep finding its way into the food supply despite the best efforts of producers and regulators.

Since breaking off from its close cousin E. coli more than 100 million years ago, salmonella has evolved into more than 2,500 strains. Some, such as Typhi, sicken humans but have no effect on other animals. Others sicken animals but not humans, with certain strains unique to a single species.

The bacterium is in so many wild animals that scientists have no hope of controlling it.

'There won't be a world without salmonella, period,' said Eduardo Groisman, a molecular microbiologist at Washington University in St. Louis. 'I haven't kept track recently, but 15 years ago when I last checked in detail, there were at least 100 different animal species in which salmonella had been isolated, from camels to cockroaches.'"